128GB Surface Pro ships with 83GB free, 64GB has only 23GB

The 64GB version of Surface Pro has 23GB of free storage out of the box while the larger 128GB version offers a bit more space at 83GB

From Engadget:

The 64GB $800 Microsoft Surface Pro comes only with 23GB of free space. that space for use. The larger 128GB version offers a bit more space at 83GB, but is still losing a massive 45GB of space to the full Windows 8 operating system and various included applications. Microsoft confirmed as much this afternoon, and issued the following the statement: "The 128 GB version of Surface Pro has 83 GB of free storage out of the box.